First branchial arch muscles

Description

The muscles that develop from the first branchial arch are closely associated with the skeletal elements that arise from the first arch, the mandible, malleus, and incus. Some of the muscles are grouped as the muscles of mastication because of their prominent role in producing the chewing movements of the jaw. There are eight muscles that arise from the first pharyngeal arch of the embryo and all of the muscles are innervated via the mandibular branch of the trigeminal nerve (cranial nerve V). The relation of the muscle attachments to the associated lever arms of the temporomandibular joint, provide these muscles with the greatest mechanical advantage of any muscle–bone system. This mechanical efficiency makes these muscles the strongest muscles in the body. These jaw-closing muscles can generate forces per unit area far in excess of any other muscle. In addition, these muscles of the first arch produce the varied array of movements that are essential for eating, speech, and other associated jaw movements. Accompanying the reduction and modification of the vertebrate jaw, two muscles, the tensor tympani and the tensor veli palatini, have assumed other functional roles linked to the soft palate and the middle ear ossicles. The tensor tympani muscle has evolved from a jaw muscle in more primitive vertebrates, to a muscle that regulates the vibratory oscillation of the auditory ossicles to help dampen loud sounds in the mammalian ear.